1. Field of the Invention
The present invention relates to an optical scanning device, a scanning optical system, a scanning imaging optical component, an optical scanning method, a ghost image preventing method and an image forming apparatus.
2. Description of the Related Art
An optical scanning device which deflects a beam from a light source by a light deflector, condenses the deflected beam toward a surface to be scanned by a scanning imaging optical system, forms a beam spot on the surface to be scanned and performs optical scanning of the surface to be scanned, is widely well-known in connection with a digital copier, an optical printer, a facsimile machine, and so fourth.
In such an optical scanning device, ideally, the surface to be scanned is scanned only by a proper scanning light. However, various optical components disposed from the light source to the surface to be scanned reflect light in some degree, and light thus reflected by these optical components and reaching the surface to be scanned acts as stray light against the proper scanning light.
Some stray light which generates a ghost image causing degradation in image quality of an image formed through the proper scanning light and is harmful is called ‘ghost light’. Generally, a ghost image generated due to ghost light has a form in which a black stripe overlaps a proper image.
Respective optical components disposed on a light path extending from the light source to the surface to be scanned may generate ghost light.
In a first part of the light path extending from the light source to the light deflector, the light path of the beam is fixed. Accordingly, it is relatively easy to prevent ghost light from being generated, by adjusting the dispositions of the optical components properly.
However, in the second part of the light path extending from the light deflector to the surface to be scanned, the light path dynamically changes as a result the beam being deflected. Accordingly, ghost light may be easily generated from unexpected parts.
As the light deflector, one which reflects the beam from the light source by a deflection reflective surface which is rotated or swung is generally used. Such a light deflector is contained in a housing in order to avoid adherence of dust to a driving part or the deflection reflective surface of the light deflector, or to avoid leakage of machine noise or air flow noise therefrom, and, via a transparent parallel plate which covers a window formed in the housing, the beam is incident on the light deflector and exits from the housing, in many cases.
In such a case, light reflected by the transparent parallel plate covering the window of the housing may become ghost light. In order to prevent the ghost light in this case from adversely affecting proper image formation, the parallel plate is inclined so that the reflected light strays in a sub-scanning direction. However, thus-straying light may become secondary ghost light as a result of being reflected by a part of the scanning imaging optical system.